1. Field of the Invention
The present invention relates to an improved transmission control device for controlling the transmission ratio of a continuously variable transmission apparatus used as an automatic transmission for a vehicle (mainly a car).
Specifically, when, while a vehicle is running, a select lever is operated to a select position in the reverse direction to the running direction of the vehicle whether such select lever operation is executed by the wrong operation of a driver or an intentional operation, the present control unit can prevent the sudden change of the vehicle behavior (for example, the sudden speed reduction, the lock of a tire, and engine failure) and the damage of the vehicle or continuously variable transmission (for example, the breakage of a propeller shaft, the breakage of the interior parts of the continuously variable transmission, the burst of a clutch), can decelerate and stop the vehicle safely and quickly, and, further, as the need arises, allows the vehicle to run according to the position where the select lever is operated. And, by realizing such transmission control, the foolproof property and failsafe property of the transmission can be secured.
2. Description of Related Art
As an automatic transmission (AT) for a vehicle, conventionally, there is widely used a stepwise variable transmission apparatus including a gear type transmission mechanism having plurality of driving modes (for example, 4 to 6 forward running gears, and 1 or 2 backward running gears). In this type of stepwise variable transmission apparatus, the transmission ratio cannot adjust continuously. That is, the transmission ratio of the stepwise variable transmission apparatus can be only stepwisely changed.
As such geared variable transmission, there are conventionally known a transmission apparatus which is composed of a torque converter and a planetary gear mechanism (an ordinary AT), and an automatic manual transmission (AMT) not only capable of execution of the transmission operation (shift-down and shift-up operation) of a step-type (manual) transmission but also capable of connecting and disconnecting a clutch using an oil pressure type or electrically-operated actuator to be controlled by a control unit.
These apparatus are disclosed in, for example:
(1) Separate Volume “Best Car” Red Badge Series 245/Book for Easy Understanding of Latest Mechanisms of Vehicles, published on Dec. 20, 2000 by Sansuisha Co. Ltd/Kodansha Co. Ltd, p. 94-95; and
(2) Aisin Seiki—Products/Enterprise “Drive Train Relation”, [online], Aisin Seiki Co., Ltd. [Retrieved on Mar. 30, 2006], Internet <URL:http://www.aisin.co.jp/product/auto/drive/index.html>
Also, a continuously variable transmission (CVT) such as a belt-type continuously variable transmission and a toroidal continuously variable transmission are becoming widely used. For example, in Japanese Patent Unexamined Publications JP-A-2004-245326, JP-A-2004-225888 and JP-A-2005-291486, there is disclosed a continuously variable transmission in which a toroidal continuously variable transmission and a gear-type differential mechanism (a planetary-gear transmission) are combined together in such a manner that the power transmission path can be freely switched by a clutch device. In a vehicle, into which such continuously variable transmission or the above-mentioned stepwise variable transmission is incorporated, according to the operation of an accelerator pedal (an opening degree of the accelerator pedal) or a running state of at that time of the vehicle obtained from the vehicle running speed (vehicle speed), not only there is carried out transmission control for adjusting the vehicle to the optimum transmission gear or transmission ratio (a target transmission gear, a target transmission ratio) but also there are executed a torque converter lock-up clutch control and a necessary clutch connecting or disconnecting control.
By the way, when driving the vehicle with the above-mentioned automatic transmission incorporated therein, because of the wrong operation of the driver or because of intentional operation of the driver, a select lever can be sometime operated to a select position in the reverse direction to the running direction of the vehicle. Specifically, in a state where the vehicle is running forward with the select position of the select lever set at the forward running position (for example, in the D or L range), according to cases, the select lever can be operated to the backward running position (for example, to R range). Also, reversely to this, while the vehicle is running backward with the select position of the select lever set at the backward running position, the select lever may be operated to the forward running position. In such case, when the transmission is adjusted to a transmission gear or a transmission ratio corresponding to the position (operation position) where the select lever is operated, and also a clutch corresponding to this operation position is connected, there is a possibility that the vehicle behavior can be changed suddenly (for example, the vehicle can be decelerated suddenly, a tire can be locked, and an engine stall can occur) and, what is worse, the vehicle and the transmission apparatus can be damaged (for example, a propeller shaft can be broken, the interior parts of the transmission can be broken, and the clutch can burst).
Of the above-mentioned inconveniences, for example, in order to prevent the inconvenience caused by the wrong operation of the driver, the select lever is structured in the following manners:
when the select lever is operated or switched from the D or L range through N range to R range, or, inversely to this, when the select lever is operated from R range through N range to the D or L range, the select lever cannot be operated linearly (with one action); or
a key-type (crank-type) shift pattern (the operation path of a select lever) is employed, or there is provided a mechanical switch separately and the select lever cannot be operated unless the select lever and switch are operated simultaneously, thereby preventing the wrong operation of the driver.
However, for example, when putting a vehicle into the garage, there is a possibility that the select lever can be operated in a state where the vehicle does not stop completely, for example, the select lever can be operated in such a manner of D range->N range->R range during the forward running of the vehicle, or in such a manner of R range->N range->D range during the backward running of the vehicle. In such case, if the vehicle is running at a low speed (for example, a speed of 5˜10 km/h or lower), it is believed that the above-mentioned sudden vehicle behavior or vehicle damage are hard to occur. For this reason, during such low speed running, even when the select lever is operated to a select position in the reverse direction to the vehicle running direction, the transmission corresponding to the select lever position operated position (operation position) is permitted, and a clutch corresponding to the operation position is connected. However, depending on the road conditions (for example, icy roads or slopes), there is a possibility more or less that the above-mentioned sudden vehicle behavior change or vehicle damage can occur.
On the other hand, for the intermediate or high speed running (for example, the running at a speed of 10 km/h or higher) of the vehicle, in order to prevent the above-mentioned sudden change of vehicle behavior or vehicle damage, there are taken the following measures:
even if the select lever is operated form N range to a select position in the reverse direction to the running direction, for example, when the vehicle is running at a preset speed or higher, transmission corresponding to the selected position is prohibited; or,
even if such transmission is executed, a clutch is not connected until the vehicle speed goes to a given vehicle speed or less.
However, there is a possibility that, in order to avoid some danger, the driver intentionally operates the select lever to a select position in the reverse direction to the running direction to decrease the speed of the vehicle or stop the vehicle while the driver dares to ignore the possible damage of the vehicle. For example, during the vehicle running along the downward slope, as the result of excessive use of braking, a brake pad and a brake disk are heated to give rise to a so called fade phenomenon that the performance of the brake is worsened (the friction force of the brake is lowered); or, the excessive generation of heat of the brake pad and brake disk causes a so called vapor lock phenomenon that air bubbles are produced in brake liquid and the brakes are thereby caused to fail.
That is, when the above-mentioned phenomenon is occurring, there is a possibility that the driver can intentionally operate the select lever to a select position in the reverse direction to the vehicle running direction. In such case, as described above, if the transmission is left prohibited or the clutch remains disconnected, unfavorably, the driver cannot decelerate and stop the vehicle.
In order to prevent such inconvenience, in the case of an automatic transmission (AMT) capable of connecting and disconnecting control of a clutch (clutch pressure control), when the select lever is operated to a select position in the reverse direction to the vehicle running direction, the automatic transmission may be adjusted to a transmission gear or a transmission ratio corresponding to the thus operated position and the clutch may be half-clutch controlled, whereby the vehicle can be gradually decelerated and finally the clutch can be engaged completely to thereby run the vehicle in such a manner as corresponds to the thus operated select lever position (power can be transmitted to the vehicle).
However, in this case, in the clutch and transmission, for example, during the forward running of the vehicle, a member rotating in a direction corresponding to the vehicle forward direction and a member rotating in a direction corresponding to the vehicle backward direction must be connected with each other. For this reason, there is a possibility that engaging members constituting the clutch can rub against each other and can be thereby worn away heavily, and also that an overload applied to the synchromesh mechanism of the transmission can cause seizure. Anyhow, in the conventional automatic variable transmission, specifically, in the stepwise variable transmission, when the above-mentioned select lever is operated to a select position in the reverse direction to the vehicle running direction, it is believed difficult that the vehicle can be switched to a running state corresponding to the selected position safely and quickly without applying a great burden to the transmission, clutch and the like.